15. The depression of the poles and other conclusive facts are certain indications that the Earth had been originally in a fluid or soft state. This state could have been caused by matter having been liquefied by fire or softened by water.

It is proverbially said: “There is no smoke without fire.” This true proverb is an application of the principle: “There is no effect without a cause.” For the same reason one can say: “There is no fire without a focus.” Now, by facts which pass under our eyes, there is not only smoke produced, but also very real fire which must have a focus. This fire coming from the interior of the Earth, and not from on high, the focus must be within; the fire being permanent, the focus must be equally so.

The heat which is augmented by measure as it penetrates the interior of the Earth, and which at a certain distance from the surface attains a very high temperature; the hot springs, so much warmer according to the depth from which they come. Fires and masses of heated and burning substances, which escape from volcanoes with vast upheavings, or by crevasses produced by earthquakes, can leave no doubt concerning the existence of an interior fire.

16. Experience demonstrates that the temperature has been raised one degree by every thirty yards of depth: whence it follows that at a depth of three hundred yards the augmentation is ten degrees, at three thousand yards, one hundred degrees, a temperature of boiling water; at thirty thousands yards, seven to eight leagues (from twenty-one to twenty-four miles), one thousand degrees; at twenty-five leagues (seventy-five miles), more than thirty-three hundred degrees, a temperature at which no known material can resist fusion. From there to the center there is still a space of more than fourteen hundred leagues (forty-two hundred miles), may be twenty-eight hundred leagues (eighty-four hundred miles), in diameter, which must be occupied by molten substances.

Although this is only a conjecture judging cause by effect, it has all the elements of probability; and one arrives at this conclusion, that the Earth is still an incandescent mass covered with a solid crust of twenty-five or more leagues (seventy-five miles) in thickness, which is scarcely the one hundred and twentieth part of its diameter. Proportionally speaking, it must be much thinner than the thinnest rind of an orange.

For the rest, the thickness of the terrestrial crust is very variable in many places; for there are some countries, especially volcanic territories, where the heat and flexibility of the soil indicate that it is much thinner. The high temperature of hot springs is also an indication of close vicinity to the central fire.

17. It is then evident that the primitive state of the softness or fluidity of the Earth must have been caused by the action of heat, not by water. The Earth was then originally an incandescent mass. In consequence of the caloric rays, it became liquefied. It has been gradually cooled, and the cooling process has naturally commenced on the surface, which has become hardened, whilst the interior has remained in a fluid state. One can thus compare the Earth to a block of coal coming red from the furnace, the surface cooling by contact with the air, although, if one breaks it, the interior is found to be yet burning.

18. At the epoch when the terrestrial globe was an incandescent mass, it contained not one atom more or less than it does today. Only under the influence of this high temperature, the greater part of the substances composing it, and which we see under the form of liquids and solids, earth, stones, metals, and crystals, were found in a very different state. They have only been submitted to a transformation. In consequence of the cooling process and mixtures, the elements have formed new combinations. The air, considerably inflated, became extended to an immeasurable distance. All the water forcibly reduced to vapor was mingled with the air. All the substances susceptible of volatilization – such as metals, sulphur, carbon – were there found in a gaseous state. The state of the atmosphere was then in no way comparable with its present condition. The density of all these vapors gave it an opacity through which no ray of sunlight could penetrate. If a living being could have existed on Earth at this period, he would have had for light only the sinister brightness of the fires beneath his feet, the burning atmosphere, and not even the existence of the sun would be noticed.